Early Dialog Replacement

An INVITE with Replaces: header can replace an early dialog. That is, a dialog where the final 2xx class response to INVITE request has not arrived yet. The Oracle Communications Session Border Controller completes the originating side of the call with a 200 OK. The original dialog with the terminator is cancelled. SDP from the new terminator can be renegotiated if it changes.

The SDP from the original 183 response is used for the 200 response back to the originator if present to complete the early transaction. If reliable provisional messages are used, then no SDP is included in the 200 response.

If no SDP is present in any of the provisional messages, then the Oracle Communications Session Border Controller constructs it from the original offer and modifying the IP port information for each c= and m= line with information from the INVITE with Replaces: header. If there are more m= lines in the original offer than ports from the INVITE with Replaces: header, then the extra ports are disabled with port value of 0. If no SDP was offered in the original INVITE, then the SDP from the INVITE with Replaces: header is used as the offer in the 200 OK.

If the SDP media parameters were compatible between the replaced and replacing SDPs, then media does not need to be renegotiated and no re-INVITE is created. If the re-INVITE fails, the original dialogs are torn down using a BYE for the original server dialog.